<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>body background fullscreen</title>
  <style>
  body {
    margin-top: 400px;
    border: 2px solid;
    text-align: center;
    color: #eee;
    background: lightcoral;
  }
  </style>
</head>
<body>
  body本身不是满屏的，它的背景会铺满屏，不区分背景是图片还是颜色
</body>
</html>